The Visionary was a Time Lady who predicted the annihilation of Gallifrey on the final day of the Last Great Time War.
Like all Time Lords, the Visionary was taken from her family at the age of eight for the selection process in the Drylands. Staring into the Untempered Schism as part of a Time Lord initiation rite, the Visionary was driven mad by what she saw in the Schism. (A Brief History of Time Lords)
She was present at a High Council meeting presided over by Lord President Rassilon during the war. She foretold that Gallifrey would burn, as she wrote Gallifreyan symbols onto a piece of paper with an ink pen.
She screamed “Gallifrey falling…Gallifrey falls!” as Rassilion’s plan to bring Gallifrey back failed at the hands of the Tenth Doctor, sending the planet back into the last day of the Time War. (The End Of Time)
By the end of the war, she was showing signs of insanity and constantly in a frantic state, spouting puzzling words and phrases which alluded to events due to happen in the future. When she was silent, the Visionary would scrawl pieces of paper with her prophecies in Gallifreyan text that was difficult to read. (The End Of Time)